Hydrogen is an ideal and non-polluting source of energy in special applications in which no conventional energy sources are available. Therefore, for instance, in devices using electric current and located in sparsely populated and rough regions, photovoltaic modules can be used for producing electric current. Such installations are frequently unmanned and require automatic or remote control operation. Also, such installations have to be operated when there is no sunlight. Storing electricity merely in batteries would require a large number of batteries, which are heavy in weight and require maintenance.
Using hydrogen for storing energy is one of the means to recover the surplus energy produced by solar cells, whereby water is decomposed into hydrogen and oxygen. Thereby, electricity may, if needed, be produced with the aid of a fuel cell from hydrogen. In order to reduce the size of the hydrogen storages required, the hydrogen must, however, be pressurized, and additional energy must be used in the pressurization.
It is known in the art to accomplish the decomposition of water into hydrogen and oxygen in electrolytic cells operating under pressure and thus producing hydrogen directly in pressurized form, so that no separate pressurization is needed. However, increased leakage is a drawback of pressurizing electrolytic cells.
It is also known in the art to place an electrolytic cell into a separate pressure shell, whereby the differential pressure between the inside and outside of the electrolytic cell substantially reduces and the leakages decrease. Thus, in an apparatus as for instance, in patent publication FR-2466515, the pressure shell is pressurized with the aid of nitrogen gas, and the apparatus comprises members for maintaining the pressure within the electrolytic cell lower than the pressure of the pressure shell. Use of separate pressurizing gas requires, however, containers for the pressurizing gases and need for supplementing the pressurizing gas. Thus, the system disclosed in the patent is not suitable for installations operating e.g. automatically in remote areas.
It is known from GB patent No. 1518234 to place the electrolytic plates inside a pressure shell, whereby the pressure of hydrogen gas prevails inside the pressure shell. However, in the design according to said patent, there is not a closed electrolyric cell placed within a pressure shell, but the electrodes used in decomposing an electrolytic liquid (HCl) are positioned to be hanging directly inside the pressure shell. The apparatus disclosed in GB patent No. 1518234 is an apparatus intended for large-scale production of hydrogen, having a great need of power, a complicated and expensive design, e.g. due to apparatus needed in purification.
In the Finnish patent application FI-923903, an electrolysis apparatus is disclosed for producing hydrogen from water; in which apparatus, an electrolyric cell is placed inside a pressure shell and in which the pressure shell is pressurized by conducting oxygen produced in the electrolysis into the pressure shell. The great compressibility of gas causes, however, that the control of the pressure may be slow because the volume of the mantle can be great, particularly if within the pressure shell also other devices are placed in addition to the electrolytic cell, such as water separators. Oxygen may, moreover cause, for instance, electrochemical corrosion in moist spaces, for instance in a space between the mantle and the electrolytic cells.